This invention relates to a turbine for internal combustion engine turbochargers and, more particularly, to a turbine which operates with greater efficiency and reliability than earlier turbines.
Turbochargers for diesel and gasoline engines are well known. Such turbochargers are being manufactured and sold by such companies as Garret Automotive Group of Allied Signal Corp., Holset Engineering Co., Ltd., Cummins Engine Co., and others. The commercially available small turbochargers generally use radial inflow turbines with the driving engine exhaust gas being directed into the turbine from vaneless volute turbine casings surrounding the small radially vaned turbine wheels of the turbines.
Such radial turbines have used open back wheels where the radial vanes of the turbine wheel extend beyond the central hub portion of the wheel outwardly and are unsupported between one another for a portion of their outer radial length. Turbine wheels of this type are typically known as open back wheels or star wheels. The omission of material to form the open back portion of the star wheel of such commercial radial turbines has been to reduce the rotational inertia of the turbine wheel and improve the transient response of the turbocharger to changes in the exhaust energy level of the internal combustion engine. Commercial radial turbines employing open back (star) turbine wheels have included the use of a stationary wall located in close proximity to the back of the rotating turbine wheel to prevent excessive gas leakage around the back of the turbine vanes. The backing member, like the turbine wheels, is exposed to the high exhaust gas temperatures of the internal combustion engine and must be made from heat-resistant material to avoid excessive distortion that may cause it to contact the rotating turbine wheel. The close tolerances needed to make such radial inflow turbines effective, and the materials and manufacturing processes necessary to obtain an effective turbine operation make such turbines expensive to manufacture.
In currently available turbochargers, the turbine blades are contoured at their outer extremities to match the contours of the turbine casing defining the turbine inlet and exit opening and exhaust passage. Generally in such turbines, the turbine blades (or vanes) extend outwardly from the central core or hub into the turbine casing portion defining the exhaust gas outlet-turbine inlet portion of the turbocharger. Where the hub diameters of the turbine blades have a small diameter, the turbine blades must be thickened at their base to withstand centrifugal force and only a small number of blades can be used, lowering the efficiency of the resulting turbine.
The radial inflow turbines of prior turbochargers have deflected the exhaust gases through 90.degree. or more in their flow between the turbine inlet and turbine outlet. Examples of such turbines are shown at page 852 of the 1990 Diesel and Gas Turbine Worldwide Catalog published by Diesel and Gas Turbine Publications, 13555 Bishops Court, Brookfield, Wis. 53005-6286.
As shown in the catalog, the "volute" portion of the turbine casing, which directs the exhaust gas from the internal combustion engine into the turbine inlet, frequently includes a meridional or central divider to direct the pulsating flow of exhaust gas from one set of cylinders of an internal combustion engine into one volute chamber and the pulsating flow of exhaust gas from another set of cylinders into the other volute chamber. The central divider of the volute maintains separation of the two pulsating flows to prevent the effect of pulsations from one set of cylinders from deleteriously affecting the flow of exhaust gas and the performance of the other set of cylinders. Such divided turbine casings are particularly desirable in V-type engines in which the flow of exhaust gas from one bank of cylinders is supplied to one part of the divided turbine casing and a flow of exhaust gas from the other bank of cylinders is supplied to the other part of the turbine casing. Such twin-flow turbine casings are shown and described in U.S. Pat. No. 3,614,259.
Commercial engines have also used turbine casings in which exhaust gas flow from two different groups of cylinders in an internal combustion engine, as for example, the two banks of a V-type engine, were carried to the turbine of a turbocharger in two separated flow paths which terminated prior to or at the start of the volute section of the casing. U.S. Pat. No. 3,930,747 describes a turbine housing of this type, which has the added advantage of being designed so that each portion of the divided manifold aspirates gas from the other portion as a result of the higher flow resulting from the pulsations, thus reducing the engine cylinder back pressure within the exhaust system.
Such prior commercial turbochargers are exemplified by U.S. Pat. Nos. 3,292,092; 3,292,364; 3,270,495; 3,614,259; 3,930,747; 3,218,029; 3,408,046; and 3,423,926.
Applicant's prior U.S. Pat. No. 4,565,505, entitled "Combination Flow Turbine for Internal Combustion Engine Turbochargers," incorporated herein by reference, describes a turbine including a meridional divider wall which directs exhaust gas from one side of the divided volute into the turbine wheel in a generally axial direction and from the other side of the divided volute into the turbine wheel in a generally radial direction. Further, while the exhaust gas from one side of the meridionally divided volute entered the turbine wheel opening axially at less than the maximum diameter of the turbine wheel, the exhaust gas from the other side of the meridionally divided volute entered the turbine wheel opening radially at substantially the maximum diameter of the turbine wheel.